The Food Lab: For The Best Sun Tea, Forget The Sun

Before we get into this, I'm going to give the quick reveal right up top for you folks who don't like to read (or skim).

For the best sun tea, don't bother with the sun.

Step 1: Combine cold water and tea in a glass or plastic pitcher at a ratio of 1 tea bag per cup of water. You can use loose tea leaves (1 1/2 teaspoon per cup) if you'd like, but save the good stuff for hot tea.

Step 2: Place the pitcher in the fridge, not out in the sun. The flavor in the end is better, and it's safer to drink.

Step 3: Wait 5 hours (more or less depending on how strong you like it).

Step 4: Discard tea bags, sweeten tea as desired, and serve over ice. Store the leftover tea in the fridge for up to 3 days.

Now the long version:

If you ask my wife, she'll confirm to you that I'm an unabashed romantic. I don't complain when she leaves in the middle of watching me play video games so she can go watch Project Runway in the other room. I'll put on clean socks and change my underwear for special occasions like tenth anniversaries and bicentennial birthdays. I even sometimes let her bite the tip off my pizza slice so long as she gives me her crust in return.

Given my affinity for blatantly schmaltzy moves like these, you'd think that I'd be a sucker for sun tea, and yes, there's an undeniable romantic appeal to the concept—iced tea brewed using the power of the sun in pretty old-fashioned glass containers. The perfect cooling sipper for hot summer days and all that. But romance is one thing and results are another.

My questions: does sun tea work? Does it really produce a better tasting or easier tea than the many alternatives? What about this whole business about never using plastic? Bags or loose leaves? Can I sweeten before I add the tea, or must I follow the advice of every Southern cookbook, blog, and grandmother out there, using only Luzianne tea bags and adding sugar only after it's brewed? And wait a minute, is the stuff even safe to drink?

On the first sunny day I could manage, I whipped out my digital thermometer, a half dozen pitchers and containers of various materials, more tea than you could shake a swizzle stick at, and got to brewing. Here's what I found.

The Tea

The idea with sun tea is simple: place tea bags (or loose tea) in a glass container filled with water and set it in direct sunlight. A few hours later, you've got brewed tea, ready to be served over a cup of ice. The story is that the heat of the sun makes tea extraction faster, giving you ready-to-drink tea within a couple hours without the need to heat up water indoors. Some folks also say that the flavor is different because of the lower temperature extraction.

Before going in depth with my testing, I first wanted to determine the optimal type of tea to use, as well as the ratio of tea to water. I brewed sun tea with both loose leaf and tea bags (for consistency's sake, everything was made with Lipton black tea), as well as the "cold brew" bags designed for quicker extraction at cool temperatures.

NOTE: The loose leaf tea pictured on the left is not actually Lipton. It's an ultra-fancy tea that Max had hidden in the closet at the office. Sorry Max. Actually taste tests were done using real Lipton tea, which I misplaced on the day photos were shot.

With these three options, what it basically all comes down to is the size of the pieces of tea leaf. Loose tea has large-ish strips of cut tea leaf, while regular tea bags contain a much finer ground mixture. Cold brew bags have the smallest pieces—nearly dust-like in appearance. While these teas are all coming from the same original source, the quality can vary quite a bit. Indeed, I talked briefly with the chief supply chain officer of Lipton, who told me that the tea destined for the iced-tea market (that is, the cold brew stuff and the tea bags sold in the Southern U.S.) is the lowest quality tea of their whole lineup; large, intact tea leaves are prized more highly by serious tea drinkers than ground leaves. So does using better tea make for better iced tea?

Tasting the brewed teas side-by-side, there was a clear difference, though even the cold brew bags produced a drink that was reliably refreshing with plenty of real tea flavor. With less extraction and fewer volatile molecules in the air, the difference between great tea and mediocre tea when we're talking cold tea is simply not as big as it is with hot tea. Save the good stuff for drinking hot. Regular old tea bags will do for our tests.

As for the ratio, I tried everything from one bag per quart up to six bags and found four per quart to be the sweet spot (that's 1 tea bag per cup of water).

Glass or Plastic?

I've read in multiple sources (including on this very site!) that only glass should be used for making sun tea, never plastic. To test this, I made tea using glass jars, heavy-duty clear polycarbonate jars, inexpensive takeout deli-style containers, as well as a completely opaque aluminum container. After brewing for 4 hours in the sun, all of the water was at roughly the same temperature (about 102°F—not hot enough to leach any unsafe contaminants off of the inexpensive plastic).

When tasted straight out of the containers, there was a definite difference. The glass and heavy duty polycarbonate was the cleanest tasting, while the plastic deli containers and aluminum container both had distinct off-flavors. However, after pouring the tea out into glasses, they were all but indistinguishable. Moral? Make your sun tea in any container you'd like, but make sure to serve it out of real glasses.

Here Comes The Sun?

For my next round of tests, I wanted to address the real big question: what exactly does the sun do for our tea? There are a number of possible answers. The most obvious is that it heats the water, and warmer water should make for more efficient extraction of flavor. It's also possible that the warmer water actually changes the shape of some of the flavorful molecules in the tea, creating flavors that simply don't exist from colder extractions. Finally, it could be that the light from the sun itself could be changing some of molecules in the tea—giving it a sunburn, if you will—affecting its flavor.

After four hours, I took the temperature of all the teas. The ones in direct sunlight (whether in clear or opaque containers) as well as the tea brewed in the water bath were all at around 102°F, in the shade it was at 75°F, indoors we got around 70°F, and in the fridge we were down at 40°F.

When tasted side by side, both sun-brewed batches and the darkened water-bath batch were all completely indistinguishable from each other, which eliminates the idea that the sun itself has some sort of magical tea-extracting properties to it. We're talking temperature here, if anything.

What about the difference between hot, warm, and cold extraction? The tea extracted with boiling water was quite clearly different from the other teas. Slightly more astringent and bitter, it tasted like exactly what it was: hot tea that had been allowed to cool. The remaining teas were much milder in flavor with more aroma and less astringency or bitterness—closer to what you want with an actual iced tea.

But here's the surprising part: between the actual sun tea, the shade tea, the countertop tea, and the refrigerator tea, there was very little difference in flavor extraction. The fridge tea was slightly paler and more dilute in flavor than the actual sun tea, but by letting the bags steep for just one more hour in the fridge, I achieved the same basic level of extraction as the tea steeped in the sun.

The difference was that the fridge-tea tasted better. Cleaner, fresher, with a balanced acidity and very slight bitterness. The actual sun tea was nearly as good, but it had a bit of the tinniness and astringency that I associate more with brewed hot tea than cool tea.

There's another issue at hand here: regular sun tea is not particularly safe. I mean, I'm no bacteriaphobe—I've stuck things in my mouth that most people wouldn't even touch with gloved-hands—but all else being equal, I'd rather go with the safer option, and the fact is, sun tea is not perfectly safe. The temperatures at which it brews is ideal breeding grounds for bacteria. Both the acidity of tea as well as its caffeine content can help to keep things at bay, but if it actually tastes better from the fridge, why take the risk?

This is also the reason why you should only sweeten your sun tea (should you choose to make it) after brewing it. Flavor-wise, it makes no difference at all, but safety-wise, it does: the sugar provides food for more rapid bacterial growth.

[Photograph: Vicky Wasik]

For some, the nostalgic and romantic appeal of brewing tea in the sun is a powerful impetus to go for the real deal, but for me, the answer's clear: Forget sun tea. For the best iced tea, brew your tea in the fridge. Not only is it safer and tastier, it also comes out cold and ready to drink.

Heck, I might even share some of my fridge-tea with my wife if she'd ever stop hogging the pizza tips.

J. Kenji López-Alt is the Chief Culinary Advisor of Serious Eats, and author of the James Beard Award-nominated column The Food Lab, where he unravels the science of home cooking. A restaurant-trained chef and former Editor at Cook's Illustrated magazine, his first book, The Food Lab: Better Home Cooking Through Science is a New York Times Best-Seller, the recipient of a James Beard Award, and was named Cookbook of the Year in 2015 by the International Association of Culinary Professionals.

He's currently raising a daughter by day, writing his second book by night (Now with 10% more science!), and is working on Wursthall, a beer hall in downtown San Mateo which will be open by the end of 2017.